Correspondence on: A Hyaluronic Acid-Rich Node and Duct System in Which Pluripotent Adult Stem Cells Circulate.

The origin of the wide spread node and duct system described by Rai et al. remains a mystery. The explanation came when another study on yolk sack hemopoiesis was compared with the "primo vascular system". It came out that the yolk sack hematogenic tissue, introduced to the embryo by the vitelline veins, does not disappear in adults, but continues to exist in form of nods and ducts along blood vessels and different organs.

Morphogens Reveal the Appearance and Functions of lncRNAs.

During the first meiotic division, the entire genetic information from DNA is transcribed into mRNPs and stored in the ovoplasm in the form of mRNP particles. The 39 human nuclear HOX proteins bind to thousands of mRNAs transcribed repeatedly by lampbrush chromosomes. HOX proteins suppress processing and translation. The RNP particles containing lncRNAs+HOX proteins are the morphogens ("transcription factors," more precisely differentiation factors), which unlock new genes and differentiate the cells of the developing embryo. All ovoplasmic mRNAs bound with HOX proteins do not translate and are noncoding. Their destination (purpose) is transportation of HOX proteins to the complementary DNAs and cell differentiation.

Stem cells: shibboleths of development, part II: Toward a functional definition.

Our previous discourse on stem cell characteristics led to the conclusion that the qualities deemed essential for a cell to be considered a "stem cell" are neither firmly established nor universally accepted, and this we accept as editorial policy. In that study, self-renewal, asymmetric division, phenotypic markers, and other attributes touted as being indicative of cells being stem cells were critically questioned as fundamental to the definition of a stem cell, leading us to seek a functional definition instead. Here, we offer further considerations, and elaborate on the characteristics that diverse investigators feel are essential for a cell to function as a stem cell, either in development or body maintenance. We hope that this discourse will promote further reflection, culminating with a definition that is widely accepted and universally applicable. We confess this goal has not been reached, neither here nor elsewhere. The outstanding goal of understanding what stem cells are, a prerequisite of characterizing what stem cells do and how they do it, is still outstanding.

The origin and development of the immune system with a view to stem cell therapy.

Careful study of the phylogeny and ontogeny of the three components of the immune system reveals that the macrophage, lymphatic, and hematopoietic systems originate independently of each other. Chronologically, the most ancient is the macrophage system, which arises in the coelomic cavity as mesenchymal ameboid cells having the properties to recognize self from non-self and to ingest foreign particles. The lymphatic system later develops from the endoderm of pharyngeal pouches, where the thymic anlage differentiates. The lymphocytes that originate here seed all lymphatic organs and retain the ability to divide and thereby form multiple colonies (lymphatic nodules) in the respiratory and digestive tract; further diversification of lymphocytes follows after confrontation with antigens. The last component of the immune system to appear is the hematopoietic system, which originates from the splanchnic mesoderm of the yolk sac as hematogenic tissue, containing hemangioblasts. The hematogenic tissue remains attached to the outer wall of the vitelline vessels, which provides an efficient mechanism for introducing the hematogenic tissue into the embryo. In an appropriate microenvironment, the hemangioblasts give rise to sinusoidal endothelium and to hemocytoblasts - the bone marrow stem cells for erythrocytes, myeloid cells, and megakaryocytes. The facts and opinions presented in this article are not in agreement with the currently accepted dogma that a common "hematolymphatic stem cell" localized in the marrow generates all of the cellular components of blood and the immune system.